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On the opening track of Christina Aguilera's latest album, the singer belts: "I'll elevate you so high I'll give you a migraine." She's got that right.

"Bionic," the 29-year-old's fourth studio release, is a disappointing album that will have listeners asking: Will the real Christina Aguilera please stand up?

When Aguilera debuted in 1999, it was a time when manufactured, bubbly faced sweethearts dominated the music scene. But she stood out from competitors like Jessica Simpson and Mandy Moore, and though she didn't sell as many records as Britney Spears, she earned more credibility -- especially with 2002's "Stripped," a defining album for Aguilera and the teen pop music era. So with "Bionic," the singer has misstepped -- and that's a shame.

The CD's lead single, the Polow da Don-produced "Not Myself Tonight," is mediocre at best, with its leather-and-chain styled music video that screams hot mess. When she sings "I'm not myself tonight," you wonder -- what day of the week is she the real Christina?

Aguilera recruited of a number of top producers and songwriters for "Bionic," and the results vary.

Producer Christopher "Tricky" Stewart falls short on the raunchy "Des Nudites," but provides the disc's best uptempo tracks with the fashion show-ready "Glam" and "Prima Donna," a thumping tune with jamming ad-libs courtesy of Lil Jon.

When Aguilera sings on the futuristic "Elastic Love," co-written by M.I.A., she proves she doesn't have enough swag to pull the song off, but she wins you over on the Linda Perry-assisted "Lift Me Up."

Where Aguilera truly shines is on the songs helmed by Australian singer Sia Furler and producer Samuel Dixon.

"All I Need" is a beautiful ode to Aguilera's 2-year-old son, while the emotional ballad "You Lost Me," about a cheating lover, is exceptional and showcases the diva's powerful voice, as does the sensitive and smooth groove "I Am."

On the latter song she sings, "Take me, free me, there will be no more pretending." Let's hope so.

CHECK THIS TRACK OUT: Like "Glam" and "Prima Donna," the male-bashing "I Hate Boys" has the right mix of energy and sass that Aguilera somewhat lacks throughout "Bionic."